Forming a pack for structure containing integer array,string list in python

Question

In C we have

struct temp
{
  unisgned int i[10];
  char a[2][10];
}temp;

Like this i am making one structure in python:

integer_aray=[1,2,3,4,5]
string_array=["hello","world"]
format_="Qs"
temp = namedtuple("temp","i a")                                      
temp_tuple =  temp(i=integer_array,a=string_array)
string_to_send = struct.pack(format_, *temp_tuple)

When i am trying like this python 2.7 giving error

string_to_send = struct.pack(format_, *temp_tuple)
error: cannot convert argument to integer

I have to send the python structure as and array of integer and as an array of strings.Is there any way we can do by sending arrays without using ctypes ?

Serge Ballesta · Accepted Answer · 2017-12-19 12:26:18Z

1

If you want to pack the equivalent of the C struct

struct temp
{
  unsigned int i[10];
  char a[2][10];
};

you will use the format "10I10s10s" where 10I stands for 10 4-byte unsigned integers in native order, and each 10s represents a byte string of size 10.

In Python3, you could write:

l = list(range(1, 11))            # [1,2,3,4,5,6,7,8,9,10]
temp = struct.pack("10I10s10s", *l, b"hello", b"world")
print(temp)

it would give (on a little endian ASCII platform):

b'\x01\x00\x00\x00\x02\x00\x00\x00\x03\x00\x00\x00\x04\x00\x00\x00\x05\x00\x00\x00\x06\x00\x00\x00\x07\x00\x00\x00\x08\x00\x00\x00\t\x00\x00\x00\n\x00\x00\x00hello\x00\x00\x00\x00\x00world\x00\x00\x00\x00\x00'

which is compatible with the C temp struct on a 32 bits little endian system.

answered Dec 19, 2017 at 12:26

Serge Ballesta

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1 Comment

rohit Over a year ago

cant we send as list of strings.or any other way using of ctypes modules or any other modules.

Lundin · Accepted Answer · 2017-12-19 12:08:02Z

0

char *a[2][10]; is a 2D array of 2x10 pointers.

You probably meant to do either char a[2][10]; which is an array of 2 C strings, each 9+1 characters long. Or perhaps char* a[2], which is two pointers to characters (possibly arrays).

answered Dec 19, 2017 at 12:08

Lundin

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1 Comment

rohit Over a year ago

yeah i required char a[2][10]

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